Caddo Lake (French: Lac Caddo) is a 25,400-acre (10,300 ha) lake and bayou (wetland) on the border between Texas and Louisiana, in northern Harrison County and southern Marion County in Texas and western Caddo Parish in Louisiana. The lake is named after the Southeastern culture of Native Americans called Caddoans or Caddo, who lived in the area until their expulsion in the 19th century. It is an internationally protected wetland under the Ramsar Convention and includes one of the largest flooded cypress forests in the United States. Caddo is one of Texas's few non-oxbow natural lakes and is the 2nd largest in the South; however, it was artificially altered by the addition of a dam in the 1900s.[2]

The Channel was used by Steamboats to reach the port at Jefferson, until water levels fell after the removal of the Great Raft.

Caddo Lake has been utilized by Native Americans for thousands of years, but substantial commercial development would only begin with invention of the steamboat and USannexation of Louisiana and Texas by treaty (Texas is the only State in the United States to have joined by treaty instead of annexation) in the 19th century. The cities of Port Caddo, Swanson's Landing, and Jefferson in Texas, and Mooringsport in Louisiana, had thriving riverboat ports on the lake. Gradually as the log jams were removed in the lake and the Red River by Captain Henry Miller Shreve and then by the Army Corps of Engineers, the lake changed shape and eventually fell over ten feet, destroying the East Texas ports and their riverboat industry.

Industry once again came to Caddo Lake with the discovery of oil beneath it. The world's first over water oil platform was completed in Caddo Lake in 1911. The Ferry Lake No. 1 was erected by Gulf Refining Company. The well bottomed at 2,185 feet (666 m) and produced 450 barrels per day (72 m3/d).[4]

Oil derricks sprang up throughout the lake, around the turn of the 20th century, further damaging the fragile ecosystem. The oil industry left Caddo for richer fields at Kilgore and other locations in Texas. Texas tried to preserve parts of Caddo in 1934 by establishing a state park, constructed by the WPA. The establishment of the Longhorn Army Ammunition Plant on the shores of Caddo, in the mid-20th century, polluted large portions of the surrounding wetlands until its closure in the 1990s. Most of the former plant site is now a federal wildlife refuge.

An ecologist named Lionel Janes conducted a survey of Caddo Lake (called Ferry Lake at the time) in 1913 and 1914. Based on an examination of cross sections of bald cypress and hardwood trees and many dead stumps he estimated that the lake came into existence sometime between 1770 and 1780.[5]

The lake is currently "under siege" by a fast-spreading, Velcro-like aquatic fern, Salvinia molesta, also known as Giant Salvinia. Accidentally introduced to the lake by boaters, the noxious weed doubles in size every two to four days, rapidly killing off life below the surface. Most of the growth of the plant is currently on the Louisiana side, where officials have been focused on recovering from damage caused by Hurricanes Katrina and Rita in 2005.[7]

Efforts at removing the weed have included biological means via beetles that normally eat the weed but cannot survive the Texas cold and now include herbicide. The Texas Water Resource Institute's Caddo Lake Salvinia Eradication Project is evaluating multiple methods of eradication. See TWRI's website for details.[8]